Conventionally, in the fields of biology, medicine and pharmacy, changes in the state of a cell and the response of a cell to a certain drug has been observed on the assumption that the average value of a cell cluster represents the characteristic of one cell. However, in reality, cell cycles rarely synchronize with one another in a cell cluster and each of the cells expresses protein at a different cycle. Although synchronous culture methods have been developed in order to solve such problems, because the cultured cells do not originate from the exact same cell, there is a possibility that different protein expressions occur due to the difference between the genes of the individual pre-cultured cells. Hence, when the response to certain stimuli are actually analyzed, it is difficult to determine whether the fluctuation in the results are caused by the response fluctuation belonging generally to the cell response mechanism or from the difference between cells (i.e., the difference in genetic information between cells). In addition, since cell strains are not cultured from one cell, for similar reasons it is difficult to determine whether the reproducibility of response to stimuli fluctuate with the difference between the genes of individual cells. Furthermore, there are two kinds of stimuli (signals) to a cell: one that is given by the quantities of signal substances, nutrition and dissolved gases contained in the solution surrounding the cell, and one that is given by physical contact with other cells. Until recently, in the research field of biotechnology, observation of a cell was done by temporarily extracting part of a cell group cultured in a large culture unit and setting it in a microscope. Alternatively, microscopic observation was performed using a microscope enclosed in a temperature-controlled plastic container, which further contains a smaller container with means to control carbon dioxide concentration and humidity. In relation to such a method, various methods have been proposed for maintaining the solution conditions during cell culture by replacing the used medium with fresh medium. For example, in the method disclosed in JP-A-10-191961, a circulation pump operates to raise the level of the culture medium above the top edge of the substrate, or lower the level of the culture medium below the bottom edge of the substrate, and maintains a constant nutritional state by supplying fresh culture medium when the level of the culture medium is low, and discharging the culture medium when the level of the culture medium is high. Further, JP-A-8-172956 discloses a structure consisting of a culture container into which is inserted an insertion tube for introducing fresh culture medium into the culture container, an extraction tube for discharging culture medium from the culture container, and a gas tube which connects the gas phase of the culture container and the pump, each comprising a filter for preventing bacteria from entering the culture container, which can maintain the nutritional state of the culture container at a constant level.
However, in spite of these proposals, a method of culturing cells while controlling the solution conditions as well as physical contact between the cells has not yet been known. In addition, a means for selecting one particular cell and culturing the single cell as a strain is not known. Furthermore, the art of controlling solution conditions and cell density in a container, or the art of culturing and observing cells while identifying cells that interact with one another has not been known, either.
As is apparent from the foregoing description, in conventional technology, cell strains do not have the exact same gene because cell culture is initiated from a cell group. Further, in conventional technology, it is difficult to select particular cells and culture the selected cells while controlling the interaction or the density of the cells. Furthermore, in conventional technology, although attempts to maintain the solution condition by replacing the culture medium is being made, it is difficult to rapidly change the environment of a particular cell that is being cultured and observe the response of that cell.
Therefore, the subject of the present invention is to solve the above-described problems of the prior art, and to provide a novel technical means for enabling: the culture of a cell group originating from a particular single cell; the culture and observation of cells while identifying cells that interact with them; and the observation of the difference between a cell to which a substance that interacts with the cells, such as a signal substance, has been added, and other cells. The invention also aims to provide novel means which enables the collection of a cell that assumes a particular state and the analysis or biochemical measurement of a gene or an expression mRNA of the cell.